Motorized liquid dispenser with an accurate dispensing volume adjustment

ABSTRACT

A liquid dispenser of the pipette type is disclosed wherein a pump plunger is reciprocated by an electric motor to discharge a predetermined volume of liquid. The volume of liquid dispensed in one operating cycle is determined by the linear stroke length of the pump plunger. The pump plunger stroke length is in turn controlled by a novel mechanism for converting the rotary motion of the electric motor into reciprocating motion of the pump plunger. Such a motion converter is described which provides a crank having an accurate and controllable separation of two points of rotation wherein an electric motor drive shaft is connected to one of the points and a reciprocating plunger mounting is driven by the other of the points.

United States Patent [1 1 Roach [4 1 Nov. 6, 1973 MOTORIZED LIQUIDDISPENSER WITH AN ACCURATE DISPENSING VOLUME ADJUSTMENT A [75] Inventor:William J. Roach, Foster City, Calif.

[73] Assignee: Oxford Laboratories, San Mateo,

Calif.

22 Filed: June 14, 1971 21 Appl.No.: 152,961

Primary Examiner-Robert B. Reeves Assistant ExaminerThomas E. KocovskyAttorneyLimbach, Limbach & Sutton [57] ABSTRACT A liquid dispenser ofthe pipette type is disclosed wherein a pump plunger is reciprocated byan electric motor to discharge a predetermined volume of liquid. Thevolume of liquid dispensed in one operating cycle is determined by thelinear stroke length of the pump plunger. The pump plunger stroke lengthis in turn controlled by a novel mechanism for converting the rotarymotion of the electric motor into reciprocating motion of the pumpplunger. Such a motion converter is described which provides a crankhaving an accurate and controllable separation of two points of rotationwherein an electric motor drive shaft is connected to one of the pointsand a reciprocating plunger mounting is driven by the other of thepoints.

3 Claims, 6 Drawing Figures PATENTED REV 6 I975 SHEET 1 or 3 FIG.|

INVENTOR. 5 WILLIAM J. ROACH ATTORNEYS PATENTEUnuv ems 3770.169 SHEET30F 3 INVENTOR.

WILLIAM J. ROACH ATTORNEYS MOTORIZED LIQUID DISPENSER WITH AN ACCURATEDISPENSING VOLUME ADJUSTMENT BACKGROUND OF THE INVENTION The presentinvention relates generally to a controllable mechanism for convertingrotary motion to a linear reciprocating motion and, more specifically,to a liquid dispensing device employing such a motion converter in amanner to control the amount of liquid dispensed therefrom.

Manually operated liquid dispensing devices of the pipette type havebeen known and used previously. An example of such a manual device forinsertion on the top of a bottle of liquid is described in US. Pat. No.3,452,901, issued July I, 1969. An improvement in such devices thatsignificantly reduces the complexity and cost thereof is described incopending U.S. Pat. application Ser. No. 103,708, filed Jan. 4, 1971. Inthis copending application, a disassemblable valve assembly is describedwherein most of the parts are constructed of an economical plasticmaterial having valve inserts made of glass.

It is highly desirable that such liquid dispensers be capable ofdispensing quantities of liquid within very narrow tolerances.Furthermore, it is desirable that such liquid dispensing devices becapable of controlling the amount of liquid dispensed with greataccuracy.

The prospects of constructing a liquid dispenser operated by a motorrather than by hand has made it necessary to take a different approachin controlling and adjusting the amount of fluid that is dispensed bythe device. Therefore, it is a primary object of the present inventionto provide a motor driven liquid dispensing device wherein the amount ofliquid to be dispensed in one cycle of operation may be accurately andsimply controlled.

SUMMARY OF THE INVENTION This and additional objects are accomplished bya motorized liquid dispenser of the present invention wherein a rotarymotion of a driving motor is converted to a linear reciprocating motionof a syringe pump plunger by a mechanism which may be adjusted tocontrol the length of the plunger stroke, thus to control the amount offluid discharged in one stroke of the pump plunger. The pump includes acylindrical barrel which is opened at one end to receive thereciprocating plunger. The other end of the pump barrel terminates in avalve mechanism which includes inlet and otutlet valves. Fluid is drawninto the pump barrel through the inlet valve during an intake stroke ofthe pump plunger and a controlled amount of liquid is discharged throughthe outlet valve of the pump assembly during a discharge stroke of thepump plunger.

The rotary to linear motion converter of the present invention whichprovides reciprocating motion to the pump plunger includes a crank bodythat is connected at one end thereof to a continuously rotating motorshaft. A mount attached to one end of the pump plunger is held on thecrank body by additional elements in a journaled relationship thereto ata controlled distance along the length of the crank body from the pointof attachment thereof to the motor drive shaft. It is this crankseparation distance that determines the stroke length of the pumpplunger and thus controls the amount of fluid that is discharged fromthe pump in a single cycle of its operation.

The additional elements which allow an easy and accurate setting of thedistance along the crank body between the motor shaft and the pumpplunger journal includes both a coarse and fine adjustment thereof foraccurately controlling the quantity of liquid discharged. The coarseadjustment includes mating teeth on one surface of the crank body and onone surface of a locking element. The locking element is movable alongthe length of the crank body when lifted slightly therefrom and forms acoarse adjustment of the crank length. A fine adjustment of the cranklength is additionally provided by a vernier cam that is rotatable withrespect to the locking element and the crank body. The vernier camcontains a cylindrical surface that is eccentrio with respect to thecenter of rotation of the vernier cam element. The pump plunger mount isjoumaled to the outside of the eccentric cylindrical surface, thereby tocause reciprocation of the pump plunger when the crank body is rotated.

An advantage of the adjustment according to the present invention isthat no wrenches or other tools are required. The setting of the strokelength of the pump plunger is practically made instantaneously by asimplehand manipulation. Accuracy and simplicity are assured by the useof separate coarse and fine adjustments. Scales are provided on thesurfaces of the adjustment elements for ready visibility on the amountof fluid that is to be discharged during each cycle of pump operation.

The entire syringe pump and valve assembly is mounted on a case whichencloses a pump driving motor. One end of this assembly is held to thecase through the pump plunger driving mechanism. The other end of thesyringe and valve assembly is preferably held to the motor case by apost to provide ready removability and to allow a certain amount ofrotation of the assembly about this post. The rotary to linear motionconverter and liquid volume adjustment mechanism is also constructed foreasy removability of the one end of the syringe and valve assembly fromthe motor case. Such easy removability from the motor case makes itpossible to use a single motor for sequentially dispensing differenttypes of fluid without first having to sterilize the syringe and valveassembly. When changing from one liquid to another, clean syringe andvalve assembly is quickly clipped into place on the motor casing.

For additional objects and advantages of the novel motorized liquiddispenser of the present invention, reference should be had to thefollowing description of a preferred embodiment thereof when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view of amotorized liquid dispenser in which various aspects of the presentinvention are employed.

FIG. 2 is an exploded view of one end of the syringe and valve assemblyof FIG. 1 which shows the elements of the rotary to linear motionconverter;

FIG. 3 is an enlarged front view of the rotary to linear motionconverter of FIG. 1 with an example of specific liquid volume dischargeamounts that may be selected;

FIG. 4 is a sectional view of the adjustable rotary to linear motionconverter taken across section 44 of FIG. 3; and

FIG. 5 is a broken view of the intake and outlet valve assemblies of theliquid dispenser of FIG. 1.

FIG. 6 is a partially cutaway view of another embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, anelectric motor, (not shown) is enclosed in a plastic casing 11.Extending from the front of the casing 11 is a toggle switch handle 13,a fuse holder 15 and a plug 17 for connection of a remote switch. Thecasing 11 is constructed with a flange portion 19 extending from thefront of the unit at its base to add stability for placing the case 1 l.on a flat surface such as a table. The motor (not shown) inside of thecase 11 can be any convenient type, preferably electrically powered.This motor drives a rotating shaft 21 (FIGS. 2 and 4) which extends fromthe front of the case 11.

A syringe and valve assembly 23, the primary operating member of theliquid dispenser, is attached to the front face of the casing 11. Thesyringe and valve as sembly 23 is attached at its top portion at a post25. The post 25 is rigidly attached to the front face of the casing 1 1and protrudes through an opening in a flange 27 of the syringe and valveassembly 23. A pin 29 snaps on to the post 25 in front of the flange 27,thereby to restrain the top portion of the syringe and valve assembly 23from falling away from the casing 11 of the liquid dispenser whileallowing a certain amount of rotation about the post 25.

The syringe and valve assembly 23 is held to the casing 11 at its lowerend by an operable connection of a crank body 31 to the rotating driveshaft 21. The drive shaft 21 is preferably attached to the rear side ofthe crank body 31 by a threaded engagement therewith. The direction ofthe threads is such that the rotation of the drive shaft 21 by the motorin the casing l 1 tightens the thread connection between the drive shaft21 and the crank body 31.

In operation of the liquid dispenser as shown in FIG. 1, rotation of themotor within the casing 11 causes a cylindrical plunger 33 toreciprocate back and forth within a cylindrical barrel member 35. Avalve assembly 3'7 is rigidly connected to the upper end of the barrel35. As the plunger 33 reciprocates back and forth in the barrel 35,fluid is alternately drawn into the syringe and valve assembly 33through an inlet opening in an intake fitting 39 and discharged throughan outlet opening of an outlet fitting 41. A portion of a flexibleplastic hose $3 is shown connected to the intake fitting 33 and isusually connected at its other end to a reservoir of the liquid to bedispensed. Similarly, a flexible plastic hose 45 is connected at one endthereof to the outlet fitting 41 of the valve assembly 37 while itsother end is terminated into a desired container such as a test tube.The outer shell of the valve assembly 37 is made of a hard plastic, andits internal structure is described in detail hereinafter with respectto FIG. 5. The plunger 33 and the barrel 35 are each made of carefullydimensioned hollow glass cylinders.

As the motor causes the drive shaft 21 to rotate, the crank body 31 isrotated, which in turn causes the plunger 33 to reciprocate up and downwithin the barrel 35. As the plunger 33 descends out of the barrel 35,fluid is drawn into the syringe and valve assembly, especially itsbarrel 35, through an inlet opening in the intake fitting 39. As theplunger 33 rises within the barrel 35 in a compression portion of itsoperating stroke,

fluid is discharged through an outlet opening of the outlet fitting 41and through the discharge tube 45 into a desired receptacle. The amountof liquid discharge in one stroke depends upon the length of thecompression portion of the stroke of the plunger 33 as it travels upwardwithin the barrel 35. This compression stroke length is accuratelyadjustably controlled by a mechanism which operably connects the plunger33 with the rotating crank body 31.

Referring especially to FIG. 2, the crank body 31 has a plurality ofperiodically recurring surface identatjons or undulations 49. Theundulations 49 effectively form a plurality of teeth in the face of thecrank body 31 which extends outward away from the face of the dispensercasing 11. A slot 51 is provided across the crank body 31 in onedirection through the area thereof occupied by the surface undulations49. A bolt 53 has a bolt head 55 that is captured by the slot 51 in amanner that the bolt 53 cannot rotate or shift axially along its length.The bolt 53 extends through the slot 51 away from the crank body 31 andis threaded at an end 57 that is furthest removed from the crank body 31and which is the end opposite of that occupied by the bolt head .55. Thebolt 53 is permitted to slide back and forth relative to the crank body31 in the slot 51. A plug 59 is provided at one end of the slot 51 toprevent the bolt 53 from slipping out of the slot 51.

A locking piece 61, having a pointer 63, has surface undulations on itsunderside that match and mate with surface undulations 49 of the crankbody 31. The bolt 53 passes through a hole in the middle of the lockingpiece 61. Therefore, it can be seen that the position of the bolt 53along the slot 51 of the crank body 31 may be fixed and locked bypressing together the mating undulations of the locking piece 61 and thecrank body 31.

A vernier cam 65 is also carried by the bolt 53 through a hole in thecenter of the vernier cam 65. The vernier cam piece 65 has formed as apart thereof a cylindrical surface 67 that is eccentric with respect tothe bolt 53. The glass plunger 33 is terminated at one end in a plasticmount and bearing piece 69. The plunger mount 69 has an opening 71 inits end furthest removed from its connection with the plunger 33. Theopening 71 is a circular one of a size to fit over the cylindricalsurface 67 of the vernier cam element 65. As the crank body 31 rotates,the cylindrical surface 67 rotates with respect to the opening 71 of aplunger mount and thus provides a journaled connection with the plunger33 to convert rotary motion into a reciprocating plunger motion. A knob73 is threaded to fit on the threaded end 57 of the bolt 53 so that itmay clamp together the crank body 31, the locking piece 61, the verniercam 65 and the plunger mount 69 during the period that fluid is beingdispensed.

The cross-sectional side view of the rotary to linear motion converterand adjustment mechanism of FIG. 4 best illustrates the operation of themotion converter which is also shown in FIGS. 2 and 3. The drive shaft21 rotates about a center of curvature 77. It can be seen from FIG. 4that the mechanism of FIGS. 2-4 provides a linearly adjustable crank.The locking piece 61 may be lifted away from the teeth 49 of the crankbody 31 and moved therealong, thereby to move the bolt 53 with respectto the drive shaft 21. This moves the cylindrical surface 67 which isthe driving member for reciprocating the plunger mount 69 and theplunger 33. R0-

tation of the vernier cam 65 about the bolt 53 also causes a translationof the cylindrical surface 67 with respect to the motor drive shaft 21.The former may be considered a coarse adjustment and the latter a fineadjustment of the linear length of a crank arm which drives the plunger33. With these two adjustments, a center 79 of the cylindrical surface67 is moved with respect to the center of rotation 77 of the drive shaft21. If these two centers of rotation are separated a distance d (FIG.4), then the plunger 37 will be reciprocated a total length in a workingstroke of 2d. As pointed out hereinabove, the coarse and fineadjustments of the linear crank arm control the amount of fluiddisplaced in a single stroke of the plunger 33 into the barrel 35 for agiven size of plunger and barrel.

The locking member 61 is oriented so that its pointer 63 lies adjacent ascale 81 (FIG. 3) that is formed along one side of the crank body 31 ina direction parallel with the direction of the slot 51 therein. FIG. 3shows a scale 81 ranging from to 18 units, the units being generallymilli-liters. The pointer 63 may be set at any one of the milli-litervolume numbers shown on the scale 81 by releasing the knob 73, liftingthe locking piece 61 from its engagement with the andulations 49 of thecrank body 31 and moving the locking piece 61 to an appropriate positionrelative to the crank body 31. This also moves the bolt 53 along theslot 51 of the crank body 31. This accomplishes a coarse adjustment ofthe fluid quantity displaced.

In order to provide a fine adjustment of the volume of liquid that isdisplaced upon one stroke of the plunger 33, a scale 83 is provided onthe face of the vernier cam 65. To accomplish this fine adjustment, thevernier cam 65 is rotated, thereby moving the center 79 of thecylindrical driving surface 67 relative to the drive shaft 21. Thismovement results from the fact that the center 79 is eccentric of thecenter of the bolt 53 about which the vernier cam 65 is rotated. In thespecific example shown in FIG. 3, the volume displaced by the dispenseris the total of the readings of the scales 81 and 83. In the settingshown in FIG. 3, the dispenser is programmed to discharge 5 milli-litersof liquid during each reciprocating cycle of the plunger 33. The use ofthe fine adjustement vernier cam 65 with its eccentric surface 67results in extremely high accuracy in the volume of liquid dispensed.

Referring again to FIG. 1, it is advantageous for many applications toprovide a control apparatus for the motor enclosed in the casing 11 thatallows either automatic continuous operation of the dispenser ormanually controlled intermittent operation. Therefore, the switch 13 ispreferably a three-position switch in which the middle position turnsthe machine off. One side of the neutral off position is spring loadedand the other side position of the switch 13 is not. When the switch 13is pushed away from the off position to the spring loaded side, themachine will dispense liquid only as long as the operator keeps theswitch handle 13 so positioned. An operator will use this position ofthe switch when he desires to fill only one or a very few containerswith liquid. When the switch is thrown in the other direction, the motorwithin the casing 11 will run continuously, and, thereby periodicallydischarge the desired liquid quantity. This continuous operation of themachine is advantageous for filling a large number of test tubes orother containers where the operator merely moves the discharge hose 45and its tip 47 from container to container in a time interval betweenthe discharge liquid pulses.

The plastic parts of the liquid dispenser described with respect toFIGS. 1-4 are constructed of an inert material such as polypropylenewhich resits the corrosive effects of the liquids which are dispensed bythe machine. The plastic parts of FIG. 2 are preferably made from aglass filled nylon material that is dimensionally stable andstructurally strong as well as being resistive to the corrosive effectsof liquids that are dispensed by the machine.

A cross-sectional internal view of the valve assembly 37 of FIG. 1 isshown in FIG. 5. Referring to FIG. 5, liquid is drawn in through aninlet opening 101 of the intake connection 39 and is discharged throughan outlet opening 103 of the outlet connection 41. The cylindrical glassbarrel 35 (not shown in FIG. 5) fits within the cylindrical plasticportion 105. A tubular housing 107 is provided with internal threads 109which cooperate with external threads of a hollow cylindrical plug 111that carries the outwardly projecting iiitake connection 39. The plug111 includes a hollow cylindrical sleeve portion 113 for receiving acylindrical sleeve 115 of a highly dimensionally stable material such asglass. The sleeve 115 is provided with a conical valve seal 117 on theinner end thereof. A spherical ball 119, preferably made of a ceramicmaterial, seats on the valve seat 117 and is held in place by a ballretaining sleeve 121 that is slidably supported within the tubularhousing member 107. The ball retaining sleeve 121 is biased toward thevalve sleeve 117 by a glass spring 123'having one end bearing againstthe closed end of the tubular housing 107 and its other end bearingagainst a radially outwardly expanding flange 125 on the ball retainersleeve 121.

A ball capturing cylindrical sleeve 127 projects from the retainersleeve 121 toward the valve sleeve 117 to hold the ball 119 in placewhen the valve assembly is first assembled. The sleeve 121 is providedof such a length that when the plug 111 is inserted into the housing107, the sleeve is only able to move a specified distance X against thespring when reduced pressure is established in the housing 107 bypumping to open the valve 119. This distance X is small enough so thatthe ball 119 will lift from the valve seat 117 but will be retainedsufficiently closer to so as not to drop from position in front of thevalve seat 117. The spring 123 is preferably made of glass so that, asan inert material, the spring is compatible with any reagent used in thedispensing device.

A tubular member 107 contains an upward projection 127 as part of anoutlet valve assembly. The projection 127 contains threads on itsoutside surface which mate with threads on the inner surface of a cap129. A hollow cylindrical sleeve 131, preferably made of glass material,is provided with a conical valve seat 133. The cylindrical sleeve 131 isheld by the upward projection 127. A spherical ball 135, preferably madeof a ceramic material, is normally biased by gravity to seat on thevalve seat 133. The outlet opening 103 is in liquid communication withthe chamber within the tubular sleeve 107 in which the ball retainersleeve 121 is fitted. On a pressure stroke of the syringe assembly, theball valve is lifted from its gravity biased position against the valvesleeve 133 and fluid is caused to flow through the outlet opening 103.

Except for the cylindrical sleeves 115 and 131, the spherical ball valve119 and 135, and the glass spring 123, the valve assembly shown in FIG.is preferably constructed of an inert plastic material such aspolypropylene. The advantage of such a construction is that the low costadvantage of plastic materials is maintained while at the same timeproviding reliability and proper functioning of the valves by the use ofa more dimensionally stable material inserted at just a few locationswithin the plastic valve assembly.

FIG. 6 shows a partially cut-away view of a dilutor attachment which maybe used in conjunction with the motorized sampler described above withrespect to FIGS. 1-5. Referring to FIG. 6, a dilutor attachment 151 isfrictionally held on the outlet 41 of the valve assembly 37 (FIG. 1) andmay be removed therefrom merely by pulling the dilutor attachment 151upward. The outside surface of the outlet 41 and an inside surface 153of the dilutor intake 155 are constructed to be of substantially thesame shape in order to complement each other to form a seal therebetweenwhen the dilutor attachment 151 is positioned on the outlet 41.

The dilutor 151 provides a direct liquid path from the outlet 41 throughits body 156 and a conduit 157 for discharge through a tip 159. The body156 has an opening 161 on a side thereof that is surrounded by acylindrical protrusion 163. A hollow cylindrical pump barrel 165 has oneend firmly inserted in the cylindrical protrusion 163. A pump plunger167 is slideably inserted in the barrel 165. One end of the plunger 167is firmly attached to a knob 169. Movement of the plunger 167 is limitedin a direction away from the barrel 165 by a band 171 that is firmlyattached to the outside of the barrel 165. The knob 169 includes a hook173 that abutts against the band 171 as the knob 169 is pulled away fromthe barrel 165. Movement of the plunger 167 in a direction into thebarrel 165 is limited by a plunger end 175 abutting against the outsidesiurface of the body 156. All parts of the dilutor attachment of HG. 6are preferably constructed of a plastic material such as polypropyleneexcept for the barrel 165 and the plunger 167 which are preferably madeof glass to form a good seal therebetween. The conduit 157 may also beof glass.

In operation of the diluter attachment, the conduit 157 is first filledwith the liquid being dispensed by the motorized dispenser of FIGS. 1 S.The plunger 167 (FIG. 6) is then in its closed position with its end 175abutted against the body 156. The tip 159 is then inserted into adifferent liquid such as a blood sample. The knob 169 is then manuallypulled outward until its book 173 abutts against the band 171. Anaccurately predetermined volume of fluid is then drawn into the barrel165, and thus the same volume of different fluid such as blood is drawninto the tip 159. The motorized dispenser is then started to dischargethe different fluid such as blood into an appropriate container alongwith a controlled amount of diluting liquid from the motorizeddispensor. The band 171 may be adjusted by the manufacturer of thedevice to individually set the volume of a different liquid that isdrawn into the tip 159 upon withdrawing the knob 169.

It will be understood that the motorized liquid dispenser of the pipettetype described above with respect to the drawings is only an example ofa device using the present invention in its various aspects and thatthis description is not limiting of the invention beyond the definitionof the appended claims.

I claim:

1. A liquid dispenser capable of discharging selected quantities ofliquid, comprising:

a rotating shaft extending through a case,

an elongated pump and valve assembly attached to said case, said pumpand valve assembly including liquid inlet and outlet openings in liquidcommunication with a pump chamber having a plunger therein, thereciprocation of said plunger causing liquid to be drawn into said pumpchamber through said inlet opening and discharge from said pump chamberthrough said outlet opening,

a crank body having a connector to receive said rotating shaft forrotating said crank body about a first axis,

a vernier cam element manually rotatable about a second axis, saidplunger being held by said vernier cam element in a manner to rotateabout a third axis that is separated a finite distance from said secondaxis, and

means connecting the crank body with the vernier cam in a manner toallow said vernier cam second axis to be displaced a linear distancealong the crank body and to allow rotation of the vernier cam about itssaid second axis with respect to the crank body,

whereby setting the linear distance displaced between the first andsecond axes is a coarse adjustment of the volume of liquid that isdispensed through the outlet valve in one stroke of the plunger, andwhereby rotation of the vernier cam about the second axis is a fineadjustment of a liquid volume so dispensed in one plunger stroke.

2. A liquid dispenser capable of discharging selected quantities ofliquid, comprising:

a liquid pump assembly including inlet and outlet openings in lqiuidcommunication with a pumping chamber having a piston therein,reciprocation of said piston causing liquid to be drawn into said pumpchamber through said inlet opening and to be discharged from said pumpchamber through said outlet opening,

a crank body capable of receiving rotary motion about a given center ofrotation, said crank body having a coarse adjustment scale extendingalong one direction from said given center of rotation,

a fastening element captured by said crank body and slidable therealongin said one direction,

means for selectively fixing said fastening element to said crank bodyalong said one direction at a desired position along the coarseadjustment scale,

a vernier cam element having a circular fine adjustment scale andattached to said fastening element for rotation aboutan axis thereof,said vernier element having an eccentric cylindrical surface with acenter axis that is displaced a distance from the axis of said fasteningelement, and

an elongated shaft journaled at one end to the cylindrical surface ofsaid vernier cam element and mechanically connected at its other end tosaid piston, whereby the piston reciprocates a stroke distance withinthe pump chamber that is controlled by the' ment and said crank body,said locking piece and said crank body having mating surfaces whichinclude a plurality of complementary surface undulations for holding thelocking piece and the crank body against relative lateral movement for aplurality of positions of said fastening element along said onedirection of said crank body.

1. A liquid dispenser capable of discharging selected quantities of liquid, comprising: a rotating shaft extending through a case, an elongated pump and valve assembly attached to said case, said pump and valve assembly including liquid inlet and outlet openings in liquid communication with a pump chamber having a plunger therein, the reciprocation of said plunger causing liquid to be drawn into said pump chamber through said inlet opening and discharge from said pump chamber through said outlet opening, a crank body having a connector to receive said rotating shaft for rotating said crank body about a first axis, a vernier cam element manually rotatable about a second axis, said plunger being held by said vernier cam element in a manner to rotate about a third axis that is separated a finite distance from said second axis, and means connecting the crank body with the vernier cam in a manner to allow said vernier cam second axis to be displaced a linear distance along the crank body and to allow rotation of the vernier cam about its said second axis with respect to the crank body, whereby setting the linear distance displaced between the first and second axes is a coarse adjustment of the volume of liquid that is dispensed through the outlet valve in one stroke of the plunger, and whereby rotation of the vernier cam about the second axis is a fine adjustment of a liquid volume so dispensed in one plunger stroke.
 2. A liquid dispenser capable of discharging selected quantities of liquid, comprising: a liquid pump assembly including inlet and outlet openings in lqiuid communication with a pumping chamber having a piston therein, reciprocation of said piston causing liquid to be drawn into said pump chamber through said inlet opening and to be discharged from said pump chamber through said outlet opening, a crank body capable of receiving rotary motion about a given center of rotation, said crank body having a coarse adjustment scale extending along one direction from said given center of rotation, a fastening element captured by said crank body and slidable therealong in said one direction, means for selectively fixing said fastening element to said crank body along said one direction at a desired position along the coarse adjustment scale, a vernier cam element having a circular fine adjustment scale and attached to saId fastening element for rotation about an axis thereof, said vernier element having an eccentric cylindrical surface with a center axis that is displaced a distance from the axis of said fastening element, and an elongated shaft journaled at one end to the cylindrical surface of said vernier cam element and mechanically connected at its other end to said piston, whereby the piston reciprocates a stroke distance within the pump chamber that is controlled by the position along said one direction of the crank body where the fastening element is fixed as well as the rotatable position of said vernier cam element, thereby to provide coarse and fine adjustments of the liquid volume discharged through the pump outlet opening during one complete stroke of the piston.
 3. A liquid dispenser according to claim 2, wherein said means for selectively fixing and fastening element to said crank body includes a locking piece carried by said fastening element between said vernier cam element and said crank body, said locking piece and said crank body having mating surfaces which include a plurality of complementary surface undulations for holding the locking piece and the crank body against relative lateral movement for a plurality of positions of said fastening element along said one direction of said crank body. 